McIlroy dragged himself to within five of the halfway lead, jointly held by Alex Smalley and Maverick McNealy at four under, with a bogey-free three-under-par 67 on Friday after his disappointing opening 74.

Only two players – Chris Gotterup with 65 and Ludvig Aberg with 66 – had shot a lower round in the championship and McIlroy’s was one of only three bogey-free rounds.

Saturday is known as moving day at the majors and McIlroy, tied for 30th overnight, needed to make a move.

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If he was looking for encouragement from the early starters, there was plenty to be had.

American Michael Kim started in extraordinary fashion, birdieing six of the first seven holes to close within two of the lead while Chris Kirk reached the eighth at five under for his round.

Rose, who only made the weekend thanks to a stunning chip-in eagle at the last on Friday, also found his touch to birdie three, four, five and six and move to one under for the championship.

Three-time major champion Padraig Harrington, 54, was also enjoying life in south-west Philadelphia as he reached the eighth at three under for his round.

Low-scoring had proved elusive over the first two days and led to a packed leaderboard, with 15 players within two shots of the American pair, as testing greens and breezy conditions at Aronimink Golf Club provided a stiff challenge to the world’s best.

It had led to questions over the course, with world number one Scottie Scheffler saying the Friday pin locations were “the hardest I have seen on tour” and McIlroy suggesting the crowded leaderboard hinted at “not a great set-up”.

The wind of Thursday and Friday, which had reached 30mph, had faded and the sun was beating down on the course, with the sweaters of Friday giving way to short-sleeves on Saturday morning.

The warm weather was set to make the undulating greens firmer and faster as the day wore on.

McIlroy teed off at 11am local time, more than three hours before the leaders, alongside five-time major champion Brooks Koepka.